This invention concerns the apparatus and processing steps for treating the flow-back and produced water and the other constituents that are used to hydraulically cause the creation of channels or fractures or fissures in hydrocarbon wells (for example, deep oil-shale deposits).
Over the centuries, people have tried different ways to take advantage of and use the inherent qualities of naturally-occurring hydrocarbon compounds to enhance his life style and cope with the many challenges of existence. For over two thousand years, the “Burning Sands” of Kirkuk, in Iraq, provided heat to Kurdish tribes, which came from the methane gas that seeped upwards from deep Geological formations to the Earth's surface only to be ignited and burn continuously to this day. Also the surface seepages of crude oil, in Pennsylvania and California, were used by the American Indians to water-proof the canoes that they used in traveling on the waterways of North America. These are only two early examples of man's utilization of natural gas and crude oil to improve his way of life.
Drake's successful drilling of a shallow crude oil well in Pennsylvania, in the late Nineteenth Century, marked the beginning of man's greatest period of economic growth driven, in great measure, by the rapid strides that were made in the exploration, production, and refining, of naturally-occurring gaseous and liquid hydrocarbon compounds. They are now used for transportation fuels, power generation, lubricants, petrochemicals, and the many thousands of other products and applications that we use in our daily lives today. The birth and development of what we now call “the Oil Industry” is one of the major principal factors and enabling driving forces contributing to the establishment and spectacular growth in the world's economy. This period of economic development is known as “The Industrial Revolution.”
During this period, many new oil fields were discovered in many parts of the world and the growth in the demand for crude oil and petroleum products grew at a fantastic rate due to the many new uses for petroleum-derived products that continued to be discovered well into the Twenty-First Century. Throughout this period the Oil Industry found many oil new fields or large deposits or reservoirs of conventionally varying hydrocarbon mixtures of liquid and gaseous compounds (both on land and offshore in the various bodies of water throughout the world). At the same time, the Industry also discovered the existence of large quantities of heavy and light hydrocarbon compound mixtures that were nonconventional in structure and were so enmeshed in the complex material matrixes that the hydrocarbon molecule compounds contained therein could not be extracted economically.
These nonconventional hydrocarbon compound sources fall into two distinctly different categories. Firstly there are the “heavy” or long-chain hydrocarbon molecule compounds such as the oil sands deposits in Canada and the heavy oil deposits in the Kern River or Bellridge regions of California or in the heavy oil belt of the Orinoco river delta region in Venezuela or the Mayan oil in Mexico where the heavy oil produced was extremely viscous and was in a semi-solid state at ambient temperatures. In these cases pour point or viscosity reduction was of primary importance. Secondly there are the “light” or “short-chain” hydrocarbon molecule compounds that are entrapped in various shale deposits throughout the United States and in many other areas in the world.
In certain countries of the world, namely in Spain, Estonia and Brazil there are large, but shallow, oil shale deposits where those countries did not have large reserves or deposits of conventional crude oil. There, a “brute force” method for the extraction of shale oil or kerogen was carried out by heating the shale rock in high temperature pressurized retorts. This practice was started as early as the nineteen twenties. The extracted kerogen or shale oil fuel was then burned in furnaces for heating purposes as well as a transportation fuel for diesel and other internal combustion engines. The extracted kerogen fuel had about the same b.t.u. fuel value and combustion characteristics as regular-grade gasoline or petrol as produced from conventional crude oil refining facilities. Those countries also did not have the necessary amount of hard currency or United States Dollars to buy conventional crude oil on the international commodities market but they did have large volumes of shale rock (although the amount of shale oil or Kerogen extracted from these shale deposits was less than four percent by weight of the shale rock itself, leaving about ninety five percent of the shale rock as waste materials). The hot condensable hydrocarbon compounds were liquefied in a conventional condensing heat exchanger unit and became the kerogen fuel. The non-condensable hydrocarbons, mainly methane, were flared or just released into the atmosphere. All these short-chain or light hydrocarbon compounds are trapped or sealed within the oil shale material matrix structure and when heated, under pressure, they are released or liberated from this matrix in a gaseous phase.
In the United States, there are many areas where oil shale rock deposits are to be found, but most of them are located as deep deposits five to ten thousand feet below the surface of the earth. As early as before the nineteen twenties, many attempts made to mine or extract the kerogen oil from stratified shale formations. Although the shale oil proved to be a very suitable hydrocarbon product, its cost of production was well in excess of the market price of similar products; thus this situation proved to be uneconomical. Additional development and investment was not justified at that time.
All of these factors and conditions have changed dramatically over the past years due, primarily, to the rapid development and exploitation of two specialized technologies. The first of these is the carefully controlled and steerable directional drilling techniques that allowed rigs to be able to initially drill vertically and then be controlled or steered to rotate into a horizontal position while drilling to a pre-determined depth. The drilling could then continue to drill well bores horizontally in the shale formation for a considerable distance. The second most important technological development was the application of an old process, namely the practice of hydraulically fracturing older vertical oil wells in order to increase the flow rate as well as to promote the further stimulation of the older, oil wells and thereby extend the economic life of the depleting oil fields.
Over the years many different techniques were developed and implemented in an attempt to extend the productive life of older oil and more mature oil field fields. Water flooding was one of the practices that was employed to maintain reservoir pool pressure in depleting oil fields as well as the injection of pressurized methane gas (when available and not being flared) in order to achieve the same result. Another technique that was tried was the use of “Shaped Charges” of explosives that were strategically placed in well casings so they could be detonated in the pay zone areas in the well bore and the force of these explosions penetrated the wall of the casing and caused fractures or fissures to be opened.
Such methods for EOR (Enhanced Oil Recovery) were the oil industry norm for many years. However some oil companies were concerned about the dangers in using explosives as a means of extending the productive life of depleting oil fields; and, in the late nineteen forties, the practice of using highly-pressured water and sand mixtures to produce fissures or fractures in the pay-zone areas began. This technique was developed to try to increase the rate of flow in the oil well and also to extend the productive life of a mature and depleting oil field without the use of explosives. Opening new channels hydraulically in the older pay zones made it easier for the liquid and gaseous hydrocarbons to flow freely under bottom hole pressure up to the surface for collection as crude oil and gas products.
Also the practice of using work-over rigs to clean out old oil well casings that had restricted hydrocarbon flows due to the accumulation of asphaltic or paraffinic compounds was wide-spread during this period.
The use of all these types of oil well stimulation practices, as well as the use of other enhanced oil recovery techniques, continued over a long period of time and many improvements were developed over the years. One of these improvements was the development of the larger capacity and more powerful barite mud pumps that were needed to assist in the drilling of deeper and deeper oil wells, both onshore as well as offshore. Some of these oil wells were drilled in water depths exceeding eight thousand feet; further drilling depths adding more than twenty thousand feet, and thus there was a need to enlarge the capacity and increase the pressure capability level of the hydraulic fracturing pumps as well.
The discovery of a number of large deposits of oil shale formations, plus the newly developed technologies of steerable directional drilling capabilities, coupled with the ability to use highly pressurized hydraulic fracturing equipment, allowed the industry to proceed with these new fracturing techniques. They were able to directionally drill, both vertically and horizontally, in the deep shale formations and then hydraulically fracture the formation to release the gaseous and liquid hydrocarbons that were contained in the shale matrix material formations. These new technologies have caused an economic “sea change” in how the world now values liquid and gaseous hydrocarbons in the global energy commodities market.
However, during the period when the application of hydraulic fracturing was becoming more wide spread, its growth, technologically and operationally, was carried out in a very haphazard, hit and miss, ad hoc manner. Many of the improvements that were made were the result of unscientifically developed trial and error attempts to improve the rate of production in an oil well as well as trying to extend the economic life of established oil fields. This was all done without the benefit of fully examining or understanding the sound scientific reasons behind the need for those improvements. The best example of this unscientific approach, in trying to solve specific processing problems, is what was occurring in the proper selection and use of various types of proppants in the hydraulic fracturing process.
After the initial pressurized water fracturing is accomplished, strong proppant materials need to remain in the fissures or fractures that are produced by the pressurized water technique if the desired increase in the flow rate of the produced hydrocarbons is to be achieved. Proppants are the selected means of “propping up” the new openings or cracks in the formations, so that they will continue to keep the new fractures or fissures open and to allow the hydrocarbon compounds to flow freely into the well bores so they can be discharged through the well head's control equipment.
Without the proper proppants that are strong enough and correctly sized to keep the fissures continuously open, the well's production rate will decline rapidly as proppant fines and softer material particles fill up the fissures. These will decrease the rate of flow and ultimately block the flow of hydrocarbons into the well bore. Many types of sands having different compositions, shapes and sizes were tested as well as many other types of proppant materials such as aluminum oxides, etc.
The key issue here is that the proper proppant that should be used in a hydraulic fracturing process is the single most important factor that is needed in achieving and maintaining the proper “voids ratio” that is needed in the pressurized water fractured channels to be able to realize the full benefit of the hydraulic fracturing process.
While these considerations are important in hydraulic fracturing in vertically drilled oil welts with selected pay zones, they are far more critical and important when applying the hydraulic fracturing process in horizontally-layered oil shale formations. As a result of the magnitude of the “Shale Gas Revolution” we are now just starting to learn more and understand more about the nature and characteristics of the various types of shale formations.
Oil shale is a form of sedimentary deposits that were laid down eons ago in the form mainly of calcium carbonates, sodium carbonates, calcium bicarbonates, quartz as well as soil materials and other compounds that became entrapped in the matrix of materials as these oil shales were being formed and ultimately deposited in the shale formations that we know about today. Many oil shale formations cross tectonic fault lines in the crust of the earth and thus can be discontinuous in their configuration. Some oil shale formations are slightly inclined in both the vertical and horizontal planes. As a result, wire line tracking as well as three dimensional seismic analyses becomes an important part of the shale gas exploration and development process.
Retrospectively it is important to recognize and stress the critical function that properly structured and sized proppants perform for the optimum extraction and production of gaseous and liquid hydrocarbon compounds which are the product as a result of the hydraulic fracturing of an oil shale deposit. This fact was not fully understood or appreciated, in the oil industry, until early in the twenty-first century. By the end of the twentieth century the Petroleum Industry had already been using the technique of hydraulic fracturing for enhanced oil recovery and oil well stimulation on producing wells for more than fifty years. All of the hydraulic fracturing operations that were carried out before the turn of the twenty first century were designed to extend the productive life of existing vertically drilled oil wells or achieve greater hydrocarbon flow rates for completed wells. All of these hydraulic fracturing operations were carried out in vertically-drilled oil wells and were fracturing pay zones that were essentially sand in composition, and were producing flowing liquid or gaseous hydrocarbons under bottom hole temperature and pressure conditions. All were in sand formations that had relatively high permeability and porosity values or good voids-ratio characteristics.
With the introduction of steerable vertical and horizontal drilling equipment together with very high pressure fracturing pumps (called by some “intensifiers”), the oil industry then applied the same hydraulic fracturing techniques that had been successfully developed and used in vertical oil well hydraulic fracturing operations and applied these same procedures to the well bores that were horizontally drilled in the deep shale formations but with less than satisfactory results. Some of the oil shale formations were more productive than others and a large number of approaches were attempted in order to try to increase the amount of encapsulated hydrocarbons that were released by hydraulic fracturing. Chemicals were added to try to control the growth of the water borne microorganisms that were impeding the flow of hydrocarbons, chemicals were also added in order to control corrosion and encrustations. Surface tension reducing chemicals were also added to try to make the fracturing water more capable of penetrating the fissures that were created by the highly pressured water. Some combination of steps were more successful in one area of oil shale than the same steps being taken and applied in another oil shale formation particularly in the difference in the percentage or amount of hydrocarbon product that was ultimately being extracted from a specific amount of hydrocarbon content in a given oil shale deposit.
It was not until the industry started to realize that the traditional principles of petroleum technology were not fully applicable to the newly developed attempts to extract entrapped liquid and gaseous hydrocarbons from mineral rock formations that did allow them to flow freely even in deep high temperature and high pressure locations. Petroleum engineers then turned to the principles of applying the examination of hard rock mechanics of minerals geology criteria in seeking a comprehensive analysis and understandable answer to these issues. Recently, research efforts proved that all shale formations could be categorized and could be roughly divided in to two distinct measurable and identifiable classifications being either a “soft shale” or a “hard shale.” See, e.g. Denney, Dennis. (2012 March). Fracturing-Fluid Effects on Shale and Proppant Embedment. JPT. pp. 59-61. The test criteria are based upon the principle of measuring the stress/strain or Young's Modulus value of a given material both before and after fracturing. The test measures the nano indentation of a mineral after applying a specific stress level. Hard shales recorded low nano indentation values while the soft shales tested measured higher indentation values. The hard shales had mainly silica, calcium carbonates, calcites, and quartz in their composition along with colloidal clays; whereas the soft shales had sodium bicarbonates, nahcolites and colloidal clay components.
The ability to accurately determine the true mineral characteristics of an oil shale is very important in selecting the best operational techniques that are needed in order to optimize or maximize the ultimate recovery of hydrocarbon components from a specific shale formation or deposit. Soft oil shale formations respond differently from hard oil shale formations after both have been subjected to the same level of hydraulic water pressure for the same soaking period of time. Hard oil shales, under high hydraulic pressures yield fissures or channels that are relatively short in penetration length and rather small in the cross sectional diameters of their fissures or flow channels. Soft oil shales, on the other hand, under the same high hydraulic pressure and soaking period yield fissures that are of greater length and have cross sectional diameters that are relatively larger than what can be achieved from the hydraulic fracturing of materials in the hard oil shale formations.
Aside from controlling the growth of microorganisms and the prevention of scale encrustations and “slick” water provisions, the most important factor in an operation's ability to extract the maximum or optimum amount of hydrocarbon from a given shale formation is the selection of the proper size and type of proppant that is carried into the fracture zone by the fracturing water. If the shale to be fractured is a hard shale the proppant must be of small enough size so that it can be carried into the small diameter fissures that are the result of the hard shale fracturing operation and strong enough to be able to keep the channel or fissure open long enough in order to allow the contained liquid or gaseous hydrocarbon product to flow freely horizontally and vertically in the well bore so as to be recoverable after being released to the surface facilities. If the proppant used is too large for the small diameter size fissure, the proppant will not penetrate into the fissure and remain there in order to keep the fissure channel open, and the amount of recoverable produced hydrocarbons will be significantly reduced. Alternatively, if an operation is hydraulic fracturing in a soft shale formation the properly sized proppant should be larger in diameter than the proppant that would be suitable for use in a hard shale. This will allow the proppant to be carried into the larger diameter fissures that are the result of the hydraulic fracturing of a soft shale. A smaller size proppant would not be as effective and this would result in a significant reduction in the amount of hydrocarbon product that could be produced.
Now that we have more scientifically measureable data regarding the differences in the various types of oil shale formations the industry now realizes, more clearly, the economic importance of selecting the proper proppant for the hydraulic fracturing of various types of oil shale formations. The best proppant for hydraulically fracturing soft mineral shales we now know is different from the best proppant that we need to use when hydraulically fracturing a hard mineral shale. Thus, there is a need for specific proppants for specific oil shales.
An object of examples of the invention, therefore, is to provide a wide range of properly sized and constituted proppants using virtually all the slurry materials that are carried to the surface and are contained in the flow-back water stream from the hydraulic fracturing of gas and oil formations.
As a result of the rapid increase in the extent and amount of hydraulic fracturing of oil shale deposits being developed in a number of different areas in the United States, there has arisen a number of ecological and environmental concerns that must be addressed if the industry is to grow successfully. For instance toxic chemicals (such as glutaraldehyde) are used as a biocide to kill, control, or eliminate, the water borne micro-organisms that are present in the water used in the hydraulic fracturing process. There is great concern such toxic chemical-bearing fracturing water could migrate into a potable water aquifer. Also of concern is the possibility of friction-reducing chemicals (e.g., polyacrylamide) or scale inhibitors (e.g., phosphonate) finding their way into and contaminating an aquifer. Detergent soap mixtures as well as chemicals such as potassium chloride are commonly used as surface-tension-reducing surfactants and could create public health issues. The current practice of injecting brine-contaminated flow-back water into disposal wells is another of concern to the public.
In some examples of traditional fracturing jobs, after explosively perforating a horizontal well casing, a water mixture is injected at high pressure into a multitude of individually sequenced fracturing zones, each being sealed off at both ends by packer sleeves. This allows the water mixture to remain in the shale formation under pressure for several days, creating channels, fractures, or fissures which, when the hydraulic pressure is released by a coiled drilling operation, allow hydrocarbon gas and liquid elements to have passageways that allow flow to the surface. For each individual fracturing zone, the pressure in the water mixture is reduced in sequence so that the depressurized water flows back horizontally into the well bore and then proceeds upward in the vertical cemented well section to the ground surface elevation. Much of the proppant remains behind in these channels; however, a significant amount comes out in the back-flow water.
The flow-back water volume accounts for less than fifty percent of the amount of injected water used for the fracturing operation. The flow-back water stream also contains materials that are leached out of the shale formation such as bicarbonates, (e.g., nahcolities). The flow-back water mixture also carries with it many volatile organic compounds as well as the micro-organism debris, any dissolved salts or brines, and a significant amount of the initially-injected proppant and their produced fines. Treatment and/or disposal of this flow-back are significant issues for the industry. For example, see Smyth, Julie Carr. (2012). Ohio quakes put pressure on use of fracturing. Associated Press. pp. D1, D6, Lowry, Jeff, et al. (2011 December). Haynesville trial well applies environmentally focused shale technologies. World Oil. pp. 39-40, 42. Beckwith, Robin. (2010 December). Hydraulic Fracturing The Fuss, The Facts, The Future, JPT. pp. 34-35, 38-41. Ditoro, Lod, K. (2011). The Haynesville Shale. Upstream Pumping Solutions. pp. 31-33. Walser, Doug. (2011). Hydraulic Fracturing in the Haynesville Shale: What's Different? Upstream Pumping Solutions. pp. 34-36. Bybee, Karen. (2011 March). In-Line-Water-Separation Prototype Development and Testing. JPT. pp. 84-85. Bybee, Karen. (2011 March), Produced-Water-Volume Estimates and Management Practices. JPT. pp. 77-79. Katz, Jonathan. (2012 May). Report: Fracking to Grow U.S. Water-Treatment Market Nine-Fold by 2020. Industry Week. U.S. App. Pub. No. 2012/0012307A1; U.S. App. Pub. No. 2012/0024525A1; U.S. App. Pub. No. 2012/0070339A1; U.S. App. Pub. No. 2012/0085236A1; U.S. App. Pub. No. 2012/0097614A1. Each of the above references are incorporated herein by reference for all purposes.
Currently, it is common practice to kill micro-organisms that are in the water mixture, either initially or insitu, by chemical or other types of biocides, so that the gaseous and liquid hydrocarbons that are trapped in the oil shale's matrix formation can flow freely into the channels and fissures vacated by the flow-back water mixture. Also, the channels created by the fracturing process must be kept open by the proppants that are initially carried into the fissures in the fracture zones by the injected water mixture. If the micro-organisms are not killed they will multiply, rapidly; and, if they remain in the fissures, they will grow and reduce or entirely block the flow hydrocarbons from these fissures. Another significant micro-organism type problem is the possible presence of a strain of microbes that have an affinity for seeking out and digesting any free sulfur or sulfur bearing compounds and producing hydrogen sulfides that must be removed from any product gas stream because it is a highly dangerous and carcinogenic material. All these types of micro-organisms must be destroyed if this type of problem is to be avoided.
In addition to the possibility of micro-organisms multiplying and blocking the flow of hydrocarbon product, the presence of dissolved solids in the water solution can also be a problem in the injected water mixture. They can deposit themselves as scale or encrustations in the same flow channels and fissures. These encrustations, if allowed to be deposited in these channels, will also reduce or block the flow of hydrocarbons to the surface. In order to avoid this condition, attempts are made in current industry practice to have the dissolved solids coalesce and attach themselves to the suspended or other colloidal particles present in the water mixture to be removed before injection in the well; however, those efforts are only partly effective. See, e.g. Denny, Dennis. (2012 March). Fracturing-Fluid Effects on Shale and Proppant Embedment, JPT. pp. 59-61. Kealser, Vic. (2012 April). Real-Time Field Monitoring to Optimize Microbe Control. JPT. pp. 30, 32-33. Lowry, Jeff, et al, (2011 December). Haynesville trial well applies environmentally focused shale technologies. World Oil. pp. 39-40, 42. Rassenfoss, Stephen. (2012 April). Companies Strive to Better Understand Shale Wells. JPT. pp. 44-48. Ditoro, Lori K. (2011). The Haynesville Shale. Upstream Pumping Solutions. pp. 31-33. Walser, Doug. (2011). Hydraulic Fracturing in the Haynesville Shale: What's Different? Upstream Pumping Solutions. pp. 34-36. Denney, Dennis. (2012 March). Stimulation Influence on Production in the Haynesville Shale: A Playwide Examination. JPT. pp. 62-66. Denney, Dennis. (2011 January). Technology Applications. JPT. pp. 20, 22, 26. All of the above are incorporated herein by reference for all purposes.
In recent years, the oil industry has tried to develop a number of ways to address these concerns. The use of ultra violet light in conjunction with reduced amounts of chemical biocide has proven to be only partially effective in killing water borne micro-organisms. This is also true when also trying to use ultra-high frequency sound waves to kill micro-organisms. Both these systems, however, lack the intensity and strength to effectively kill all of the water-borne micro-organisms with only one weak short time residence exposure and with virtually no residual effectiveness. Both systems need some chemical biocides to effectively kill all the water borne micro-organisms that are in water. Also, some companies use low-frequency or low-strength electro-magnetic wave generators as biocide/coalescers; however, these too have proven to be only marginally effective.
Therefore, an object of further examples is to economically address and satisfactorily resolve some of the major environmental concerns that are of industry-wide importance. Objects of still further examples are to eliminate the need for brine disposal wells, eliminate the use of toxic chemicals as biocides for micro-organism destruction, or for scale prevention, and the recovery of all flow-back or produced water for reuse in subsequent hydraulic fracturing operations. Examples of the invention provide technically sound and economically viable solutions to many of the public safety issues that have concerned the industry in hydraulic fracturing.